Lecture 8: Reproductive behaviour Flashcards
Genetic basis of sexual differentiation
- more info carried X
- Y function = control development of glands that produce the male sex hormones
Genetic determination of sex
- M&F same until 6 weeks
- presence/absence of Y chromosome that leads to development of either M/F gonads
Wolffian duct
-has capacity to develop into male reproductive system
Mullerian duct
-has capacity to develop into female reproductive system
SYR
- week 7
- gene of Y causes formation of gonads into testes
- absense allows gonads to develop into ovaries
- female gender is default setting until enzymatic activity
Internal sexual differentiation male
XY: with testicular hormones and mullein duct inhibiting substance
- male system develops and female system dissipates
- Anti-mullerian= defeminising
Androgen=masculating hormone
Internal sexual differentiation Female
XX: without testicular hormones
- ovaries dont release hormones at the stage
- lack of other hormones that cause male system to break down and Mullerian system develops
Androgen insensitivity syndrome
- genetically male XY
- lack of testosterone not helping the male system to develop
- non/low functioning androgen receptors
- wolffian system retarded
Persistent mullerian duct syndrome
- genetic male
- no anti-mullerian hormone not allowing female system to dissipate so both sets of gender organs are developed
Sexual differentiation
External
-external sex organs develop at 8-12 weeks due to presence or absence of testosterone and anti-mullerian hormone
T= male organs
No T=female organs
Puberty
- 10.5 for girls
- 11.5 for boys
- increase in release of hormones by the anterior pituitary gland
- increase in GnRH and adrenocorticotropins lead to the release of gonadotropic hormones from the gonads and adrenaline cortex (LH and FSH)
- these hormones lead to secretion of six hormones from the gonads which causes maturation of the genitals and development of secondary sex characteristics
What happens in puberty
Males
-androgen levels are higher than oestrogen leading to masculisation
Females
-estrogen hormones are predominate
**people castrated before puberty dont become sexually mature unless receive replacement injections
Bi-potentiality of secondary sex characteristics remains throughout life –
males given estrogen to treat tumour = breasts and fine facial hair
women with androgen secretion from a tumour = beard and lowered voice
Hormonal control of sexual behaviour
- Sexual behaviour of male animals (non-primate) depends on testosterone (secreted by testes)
- Female (non-primate) sexual behaviour depends on estrus cycle (increase in estradiol followed by progesterone)
Influences of sex hormones on human behaviour
- Sexual initiation in females but not males is associated with menstrual cycle
- GnRH antagonist reduces sexual interest, fantasy and intercourse in young males
- Anticipation of sexual activity can increase testosterone levels in men
- Testosterone levels in women and men affects and is affected by sexual behaviour
- Behaviour can influence hormones just as hormones can influence behaviour
Pheromones
*Hormones carry messages from the secreting gland to target tissue within an organism
Carry messages between animals
via olfaction (sniffing or tasting)
• Vomeronasal organ → olfactory
bulb → medial nucleus of amygdala
• Mostly present in sweat or
urine
Lee-boot effect
The slowing and eventual cessation of estrous cycles in groups of female animals that are housed together; caused by a pheromone in the male animal’s urine.
Coolidge effect
The restorative effect of introducing a new female sex partner to a male in refractory period after sexual activity; caused by a pheromone in the female animal’s urine
Whitten effect
The synchronization of the menstrual or estrous cycle of a group of females, which occurs only in the presence of a pheromone in a male’s urine.
Vandenbergh effect
The earlier onset of puberty seen in female animals that are housed with males; caused by a pheromone in the male’s urine.
Bruce effect
Termination of pregnancy caused by the odour of a pheromone in the urine of a male other than the one that impregnated the female.
Human pheromones?
- Female menstrual cycle
- Female groups – nuns, single-sex colleges (McClintock, 1971) cycles sync
- Underarm perspiration study (Russell, Switz and Thompson, 1980) donor of sweat and recipient cycled synced
- Male groups shorten cycle – armed forces
- Male and female body odour can be distinguished
- Female body odour rated as more pleasant and “sexy” during ovulatory (fertile) phase
- Pheromones or sensory signals?
- Human vomeronasal organ inactive (sparse receptors)
- Standard olfactory system may be able to detect Pheromones
- Detection of odours can be unconscious
Sexual orientation
Prenatal hypothesis
Male homosexual = not masculinised or defeminized
Female homosexual= masculinised but not de-feminized
Bisexual= masculinised, not defeminized
Support prenatal hypothesis –CAH disorder
-Androgen insensitivity syndrome
- females adrenal gland secretes excessive amounts of androgens
- These individuals are genetically male (XY) but have female external genitalia (no defeminising) - usually have the testes removed surgically and live as women (with treatment of female hormones in adulthood).
Neural control of sexual behaviour Males
•Medial preoptic area (MPA)
- area of cell bodies just rostral to the hypothalamus
- Electrical stimulation induces copulatory behaviour/ copulation increases activity in this area/ destruction of MPA abolishes sexual behaviour
- Sexually dimorphic nucleus (SDN) - Size of structures of neurons in MPA dependent on prenatal androgen exposure
- MPA receives input from vomeronasal organ (pheromones) possibly explaining the effects of female pheromones on male rodents
- MPA controls sexual motor reflexes and receives incoming information from stimulation of the genitals
Neural control of sexual behaviour Females
- Ventromedial nucleus of the hypothalamus (VMH)
- A large nucleus of the hypothalamus located near the walls of the third ventricle
- Lesions to this area stop the display of lordosis in female rodents and electrical stimulation facilitates sexual behaviour
- VMH receives input from vomeronasal organ (pheromones)
- VMH controls sexual motor reflexes via Periaqueductal Gray Matter
- Female sexual activity is activated by a priming dose of estogen followed by progesterone and injection of these hormones into the VMH stimulates sexual behaviour
Hormonal control of maternal behaviour
- no evidence of organisational effect of hormones play a role
- maternal behaviour is affected by hormones but not controlled by them
Neural control of parental behaviour: Maternal
- Medial preoptic area (MPA) plays most critical role
- Lesions of this area disrupted both nest building and pup care – mothers simply ignored their offspring (Numan 1974)
- Most species of mammals are cared for by mothers but a few species of rats share task of infant care
Neural control of behaviour: Paternal
• Brains of these nurturing fathers show some interesting differences to nonpaternal fathers of other species
• Size of MPA shows less sexual dimorphism in
monogamous voles than promiscuous voles
• Increased Fos production when male prairie voles
were exposed to a pup
• Lesions of MPA produce severe deficits in paternal behaviour in rats
